Hello there,
Did you try checking the health of the S2D disks?
Maybe one of the disks is in an unhealthy state and hence you are getting this error message as this disk is not considered operational when trying to remove the disk.
Every storage pool has a health status - Healthy, Warning, or Unknown/Unhealthy, as well as one or more operational states.
Troubleshoot Storage Spaces and Storage Spaces Direct health and operational states https://learn.microsoft.com/en-us/windows-server/storage/storage-spaces/storage-spaces-states
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